Former head of MI5 declares 42-day detention plans are 'unworkable'

Criticism: Baroness Manningham-Buller dismissed Government plans for 42-day detention without charge as 'unworkable'

The former head of MI5 yesterday condemned Gordon Brown's anti-terror laws as 'unworkable'.

Baroness Eliza Manningham-Buller dealt a major blow to the Prime Minister's authority by savaging plans to hold terror suspects for 42 days.

In her maiden speech to the House of Lords, she said the proposals were flawed on a 'practical basis as well as a principled one'.

She spoke as a former police chief said locking up suspected extremists without charge would 'inflame terrorism'.

The ex-spy chief's first public words on the row piled fresh pressure on Downing Street. Mr Brown faces a crushing defeat when the Lords votes on extending pre-charge detention from the current 28 days later this year.

He narrowly avoided disaster last month when the measure limped through the Commons with the help of the Democratic Unionists. But Lady Manningham-Buller's intervention gives Mr Brown a fresh headache as it could embolden wavering Labour MPs to oppose the plans.

Speaking on the Counter-Terrorism Bill, the director-general of Britain's security service until April last year, said: 'I have weighed up the balance between the right to life - the most important civil liberty - the fact that there is no such thing as complete security, and the importance of our hard-won civil liberties.

'Therefore on a matter of principle, I cannot support 42 days pre-charge detention. I don't see on a practical basis, as well as a principled one, that these proposals are in any way workable.'

In what will be interpreted as a barbed swipe at Mr Brown's 'buying off' of the DUP, Lady Manningham-Buller said national security 'should be above party politics'.

Crossbench peer Lord Dear, a former chief constable of West Midlands Police, warned the proposals would act as 'a recruiting sergeant for Al Qaeda by alienating British Muslims.

Lord Falconer, a Lord Chancellor under Tony Blair, urged the Government to ditch 42-day detention. The former cabinet minister - who backed an unsuccessful bid for 90 days in 2005 - told peers it would provide 'no advantage' to fighting terrorism.

Labour's Lord Goldsmith, an Attorney General under Mr Blair, also said he could not back 42 days claiming it 'undermined fundamental freedoms'.

The debate came ahead of tomorrow's Haltemprice and Howden by-election which was triggered by former shadow home secretary David Davis's resignation after the vote on 42 days.

Six out of ten people believe terror suspects should not be held without charge for more than 28 days, according to the Joseph Rowntree Reform Trust.

Conservative Party leader David Cameron joins David Davis for the campaign trail during the Haltemprice and Howden by-election, which was called after Mr Davis' resignation on an 'erosion of civil liberties' platform